1. Field of the Invention
This invention relates generally to carpets and the like, and is more particularly concerned with a tufted carpet having a double primary backing for providing a dimensionally stable carpet before coating, and without application of a secondary backing.
2. Discussion of the Prior Art
In the past, tufted carpeting was made by tufting yarn into a backing of woven jute or the like. The jute backing was heavy and stable, so one coated the back with latex or other adhesive only to lock in the tufts, and the carpet was ready to install. More recently, however, various light weight materials have been used as a primary backing through which yarn is tufted, and a secondary backing of a stable material is adhered to the back of the carpet by an adhesive.
Currently, the most popular primary backings are polypropylene, either woven or non-woven materials. Such backings are preferred because: they are inexpensive; the material has an oily quality that provides for smooth entry and exit of the needles; and, the material is quite elastic so the hole tends to close around the yarn after the needle is withdrawn. However, the polypropylene has some disadvantages. Those skilled in the art will realize that polypropylene is a thermoplastic-elastomer, so the backing is subject to degradation by excess heat, and is rather easily stretched through the application of tension.
Typically, after face yarns are tufted into a primary backing, the resulting carpet is back coated with an adhesive to lock in the stitches. Without the back coating, the tufts are very easy to pull out, so the back coating is an important next step. During the coating, however, the carpet is unstable because there is only the primary backing. Thus, one experiences generally from 5 to 20% elongation of the carpet during the back coating process. While this creates more carpet, it also reduces the amount of face yarn per unit area. Furthermore, the backing may not stretch uniformly, so any pattern in the carpet will be distorted. There have been efforts at holding the pattern straight, but such efforts require additional equipment and effort, and still do not solve the basic problem of stretching of the primary backing.
The prior art includes some rugs or carpets having a plurality of backings. For example, U.S. Pat. No. 2,713,012 to Hartstein discloses a tufted rug having dual primary backings of cotton and jute or the like. The Hartstein patent does not contemplate back coating of the rug, and relies on the double backing to assist in holding in the tufts. Also, the jute backing is heavy enough to stabilize the rug. U.S. Pat. No. 4,426,415 to Avery discloses a carpet in the nature of artificial turf having a plurality of primary backings, the backings varying in fineness from bottom to top of the carpet. All of the plurality of backings are of the same material, and polypropylene is specifically mentioned. Since Avery contemplates back coating of the carpet, the problem of stretching and distorting will still be present, though perhaps slightly reduced because of the greater strength of multiple backings. U.S. Pat. No. 4,705,706 to Avery discloses a multiple primary backing, but the backing may be nylon or the like while the face yarn is polyethylene so the back stitch can be set by heat rather than by a separately applied adhesive. The multiple layers of backing, then, allow sand to infiltrate when the carpet is used as outdoor turf.
It will therefore be seen that the prior art has not provided a solution to the problem of stretching and distorting of the carpet during back coating and other treatment of the carpet.